Recently, organic EL elements have been actively developed. Display devices using organic EL elements need neither backlights nor polarizers, and have a wide dynamic range and a wide viewing angle, which is advantageous for reduction in thickness and cost. Thus, the organic EL elements have been expected to be used in next-generation display devices.
In typical organic EL elements, an organic EL layer that emits light in response to application of a voltage is provided between a thin-film like anode and a thin-film like cathode, and a hole injection layer, a hole transport layer, a light emitting layer, a hole blocking layer, an electron transport layer, etc. are stacked in the organic EL layer.
These layers in the organic EL layer are often formed by vacuum deposition (a vacuum deposition method), but in some cases, are formed by coating using spin coating etc. (a coating method).
In order to display a color image on organic EL display devices, three sub-pixels of red (R), green (G), and blue (B) are typically arranged in each pixel, and light emission of the sub-pixels is controlled. This method requires a light emitting layer that emits light of each color to be selectively formed in each sub-pixel (patterning).
However, a patterning technique capable of being used in practical applications has not been established in the field of organic EL display devices. In particular, there has been a problem in a process for increasing the size of the display devices.
Some techniques have been proposed as this type of patterning technique (Patent Document 1 etc.).
(1) Patent Document 1
A metal mask having holes is used. Patterning is performed through the holes of the metal mask by vacuum deposition (a mask deposition method).
(2) Non-Patent Documents 1-3
A transfer substrate is used on which a photothermal conversion layer that converts laser light to thermal energy and a light emitting layer are formed on its entire surface. With the transfer substrate being placed to face a transfer target substrate, a predetermined area of the transfer substrate is irradiated with laser. Thus, only the light emitting layer in the irradiated area is transferred to the transfer target substrate (a laser transfer method).
(3) Patent Document 2
Small droplets are dropped onto predetermined positions to form a thin film (an ink jet method or IJ method).
(4) Patent Document 3
A transfer substrate having light emitting pigments of RGB arranged thereon is used as a substrate that allows laser light to pass therethrough. The transfer substrate is externally irradiated with laser light, thereby transferring the light emitting pigments by using heat generated by the laser light. All the light emitting pigments are simultaneously formed on the transfer substrate. An IJ method or a vacuum deposition method is used to form the light emitting pigments.
(5) Patent Document 4
A first transfer layer containing a first organic material and a second transfer layer containing a second organic material are patterned on a transfer substrate via a photothermal conversion layer by a printing method. The transfer layers are simultaneously transferred to a transfer target substrate by irradiating this transfer substrate with radiation.